Water-cooled rotary piston engine



y 16, 1967 YOSHITSUGU HAMADA 3,319,612

WATER-COOLED ROTARY PISTON ENGINE Filed Sept. 27, 1965 INVENTOR S//fiuju fi am d ATTORNEY-5 United States Patent Ofifice 3,319,612 Patented May 16, 1967 3,319,612 WATER-COGLED ROTARY PISTON ENGINE Yoshitsugu Hamada, Nagahama-shi, Japan, assignor to Yanmar Diesel Engine Co., Ltd., Osaka, Japan, a corporation of Japan Filed Sept. 27, 1965, Ser. No. 490,228 Claims priority, application Japan, Sept. 30, 1964, 39/ 76,342 3 Claims. (Cl. 1238) This invention relates to water-cooled rotary piston engines of the type including a housing comprised of a shell, the inner surface of which has a multi-lobed profile approximating an epitrochoid, and end walls secured to said shell at its opposite ends, an engine shaft extending axially through said housing and having an eccentric portion between said end walls thereof, and a piston mounted on said eccentric portion of said engine shaft and adapted so as to rotate in the same direction as said engine shaft at a predetermined revolution ratio thereto, said piston having an approximately polygonal transverse cross section defining apex portions slidable along the inner surface of said shell.

Previously, this type of rotary piston engine has generally included a cooling system in which cooling oil is circulated through the interior of the piston for the purpose of cooling the latter.

Also with this system, oil scraping rings are usually employed and are mounted on the piston so as to slide over the adjacent end walls of the engine housing maintaining pressure contact therewith. By this arrangement, however, it has been impossible to completely prevent oil leakage.

In addition, the sliding contact of the oil scraping rings with the end walls of the engine housing causes substantial resistance to the rotation of the engine shaft and makes it more ditlicult to start the engine by human effort. Further, the conventional cooling system has necessarily included a feed pump for circulating oil through the piston, an oil reservoir for storing oil discharged from the piston, and an oil strainer, which is necessary where the lubricant oil, used for lubrication of the engine shaft hearings, is utilized as a cooling medium according to the general practice. Accordingly, in cases where this type of engine is used, for example, as an outboard motor, it compares unfavorably in weight and cost with a conventional two-cycle reciprocating engine because of the need for extraneous accessories, as mentioned hereinbefore.

To eliminate this deficiency, the present invention proposes to attain the purpose of cooling the piston principally by heat transmission through gas seals secured to the piston so as to provide sliding engagement with the end walls of the engine housing and partly by dissipation of heat from the piston to the fuel-air mixture, which is circulated through the piston.

With engines of the type with which the present invention is concerned, the shell and end walls of the engine housing include so-called hot areas which are continuously exposed to highly heated gases and never cooled by suction air. On the other hand, the piston is alternately exposed to the highly heated gases and the cold suction air, thus having a low heat load compared to the housing.

Accordingly, it is proposed to cool with water the shell and end walls of the housing, which have a higher heat load, and to resort solely to gas seals and the fuel-gas mixture for cooling the piston, which has a lower heat load.

The proposed system of cooling the piston, however, inherently involves the following deficiencies. First, the piston itself is held at a temperature somewhat higher than that obtainable when oil-cooled. and this causes a 'se in the temperature of the bearings supporting the piston and reduces the service life of the hearings. Secondly, circulation of the sucked gaseous mixture through the piston, which has a planetary motion within the housing, reduces the charging efiiciency of the engine. These deficiencies can be effectively eliminated so as to make the proposed cooling system practically feasible by the following measures. Namely, the first-mentioned deficiency can be eliminated by throttling the heat flow from the rotor to the outer race of the bearing while the second-mentioned deficiency can be eliminated by forming the passage of the gaseous mixture so as not to disturb its flow through the piston.

The present invention will next be described in further detail with reference to the accompanying drawing, in which.

FIG. 1 is a vertical cross-sectional view of one embodiment of the present invention;

FIG. 2 is a horizontal cross-sectional view of same taken substantially along the line A-A in FIG. 1;

FIG. 3 is an enlarged fragmentary cross-section taken substantially along the line B-B in FIG. 2;

FIG. 3a is a diagram illustrating the relative velocity of the gaseous mixture in FIG. 3; and

FIG. 4 is a fragmentary enlargement of a portion of FIG. 1.

Referring to the drawing, the rotary piston engine illustrated and, which embodies the present invention, includes a housing comprised of a shell 1, the inner surface of which has a multi-lobed profile approximating an epitrochoid, and end walls 3 and 5 secured to said shell at its opposite ends. An engine shaft 7 extends axially through the engine housing and has an eccentric portion 7a. Mounted on the eccentric shaft portion 7a, by way of a bearing 11, is a piston 9 which carries an internal gear 15 thereon. Secured to one of the end walls 5 is a pinion gear 13 which is in meshing engagement with the internal gear 15 so as to allow rotation of the piston at a predetermined revolution ratio to the engine shaft and in the same direction as the latter.

Water is circulated for the cooling purpose through a Water jacket 17 formed in the housing shell 1 and water jackets I19 and 21 formed in the respective housing end walls 3 and 5.

Each of the arcuate surfaces of the piston defines a working chamber 23 together with the epitrochoidal inner surface of the housing shell 1 and, with rotation of the piston 9, the working chamber 23 increases in volume to reduce the pressure therein to a vacuum. Accordingly, by providing a suction passage 25 in one of the end walls 3 of the housing and respective passages 27 and 29 in the piston and the other end wall 5, it is possible to suck a gaseous mixture of air and fuel including lubricant oil from the exterior of the engine into the working chamber 23. 1

In the triangle of the velocity diagram of FIG. 3a, the vector Vm indicates the average velocity of the gaseous mixture, the vector U indicates the average peripheral speed of the piston 9 and hence vector V indicates the velocity of the gaseous mixture in the piston relative there- [0.

Therefore, by forming the passage walls 31, 33 and 35 ('FIG. 3) in a manner so that the passage 27 in the piston 9 coincides in direction with the relative velocity of the gaseous mixture, its circulation through the piston 9 can be made smooth so as to prevent any disturbance in the flow of the mixture and hence reduction in charging efticiency of the engine. Such circulation of the cold gaseous mixture through the piston 9, together with the heat dissipation through the gas seals 37 secured thereto, is effective in cooling the piston. On the other hand, the gaseous mixture, flowing through the passages 25 and 29 formed in the end walls 3 and 5 of the housing and through-the passage 27 formed in the piston 9, serves to lubricate the bearings 39, 41 and .11 effectively, since it includes a proportion of lubricant oil as described hereinbefore Moreover, since the piston 9 is held at a temperature somewhat higher than for oil-cooled in the conventional manner, some measure must be taken to prevent any substantial amount of heat from being transmitted from the piston to the bearing 11 so as not to raise its temperature to any considerable extent. To meet this requirement, the outer bearing race 111a (FIG. 4) is formed in its outer periphery with a peripheral groove 11b of a substantial width to reduce the area of contact of the race 11a with the piston. By this means, the flow of heat from the piston 9 through the area of contact is effectively throttled and thus the bearing race 1=1a can be safely kept from being heated to any elevated temperature.

Having fully described my invention, it is to be understood that I do not wish to be limited to the details set forth, but my invention is of the full scope of the appended claims.

What is claimed is:

-1. A water-cooled rotary piston engine of the type including a housing comprised of a shell, the inner surface of which has a multi-lobed profile approximating an epitrochoid, and end walls secured to said shell at its opposite ends, an engine shaft extending axially through said housing and including an eccentric portion between said end walls thereof and a piston mounted on said eccentric portion of said engine shaft and adapted to rotate in the same direction as said engine shaft at a predetermined revolution ratio thereto, said piston having an approximately polygonal transverse cross section defining apex portions slid'able along the inner surface of said shell, means for water-cooling said shell and end walls of said housing and means for circulating a fuelair mixture through said piston.

2. A water-cooled rotary piston. engine as claimed in claim 1 in which said piston provides passages of the fuel-air mixture formed to coincide in direction with the relative direction of the flow of said mixture passing through the piston.

3. A water-cooled rotary piston engine as claimed in claim 1 in which an antifriction bearing for mounting said piston on the eccentric portion of said engine shaft is provided, the outer race of which being provided in its outer periphery with a peripheral groove of a substantial width.

References Cited by the Examiner UNITED STATES PATENTS MARK NEWMAN, Primary Examiner.

R. D. BLAKESLEE, Assistant Examiner. 

1. A WATER-COOLED ROTARY PISTON ENGINE OF THE TYPE INCLUDING A HOUSING COMPRISED OF A SHELL, THE INNER SURFACE OF WHICH HAS A MULTI-LOBED PROFILE APPROXIMATING AN EPITROCHOID, AND END WALLS SECURED TO SAID SHELL AT ITS OPPOSITE ENDS, AN ENGINE SHAFT EXTENDING AXIALLY THROUGH SAID HOUSING AND INCLUDING AN ECCENTRIC PORTION BETWEEN SAID END WALLS THEREOF AND A PISTON MOUNTED ON SAID ECCENTRIC PORTION OF SAID ENGINE SHAFT AND ADAPTED TO ROTATE IN THE SAME DIRECTION AS SAID ENGINE SHAFT AT A PREDETERMINED REVOLUTION RATIO THERETO, SAID PISTON HAVING AN APPROXIMATELY POLYGONAL TRANSVERSE CROSS SECTION DEFINING APEX PORTIONS SLIDABLE ALONG THE INNER SURFACE OF SAID SHELL, MEANS FOR WATER-COOLING SAID SHELL AND END WALLS OF SAID HOUSING AND MEANS FOR CIRCULATING A FUEL-AIR MIXTURE THROUGH SAID PISTON. 